A team of scientists largely from Arizona State University (ASU) now show that what has been called lonsdaleite is in fact a structurally disordered form of ordinary diamond.

"So-called lonsdaleite is actually the long-familiar cubic form of diamond but it is full of defects. These can occur due to shock metamorphism, plastic deformation or unequilibrated crystal growth," explained Piter Nemeth, a former ASU visiting researcher.

The lonsdaleite story began almost 50 years ago. Scientists reported that a large meteorite called Canyon Diablo, after the crater it formed on impact in northern Arizona, contained a new form of diamond with a hexagonal structure.

They described it as an impact-related mineral and called it lonsdaleite - after Dame Kathleen Lonsdale, a famous crystallographer.

Since then, lonsdaleite has been widely used by scientists as an indicator of ancient asteroidal impacts on Earth, including those linked to mass extinctions.

The scientists re-examined Canyon Diablo diamonds.Using the advanced electron microscopes, the team discovered, both in the Canyon Diablo and the synthetic samples, new types of diamond twins and nanometer-scale structural complexity.

The outcome of the new work is that so-called lonsdaleite is the same as the regular cubic form of diamond but it has been subjected to shock or pressure that caused defects within the crystal structure.